1. Technical Field
The present invention relates to a flexible transparent electrode for a dye-sensitized solar cell and a method of manufacturing the same, and, more particularly, to a flexible Ti—In—Zn—O transparent electrode for a dye-sensitized solar cell and a method of manufacturing the same, and to a metal-inserted three-layer transparent electrode with high conductivity using the flexible transparent electrode and a method of manufacturing the same, wherein compared with the conventional fluorine-doped tin oxide (FTO) and indium-tin oxide (ITO) transparent electrodes with high deposition temperature, the flexible transparent electrode, despite being deposited at room temperature or low temperature, has low surface resistance, high conductivity and transmittance, superior resistance to external bending, improved surface characteristics and better surface roughness performance.
2. Description of the Related Art
Typically, a dye-sensitized solar cell is a kind of solar cell which causes chemical power generation using the ability of a dye to absorb solar light, and generates power by absorbing wavelengths at about 400˜800 nm among solar light having wavelengths from 300 nm to 2,500 nm.
FIG. 1 is a cross-sectional view schematically illustrating a conventional dye-sensitized solar cell, in which a typical dye-sensitized solar cell includes a transparent glass substrate, a photoelectrode (an anode) including a metal oxide and a dye, an electrolyte, and a counter electrode (a cathode).
The photoelectrode which is provided in the form of a porous membrane is made of an n-type transition metal oxide semiconductor having a wide bandgap, such as TiO2, ZnO, or SnO2, and a monolayer of a dye is adsorbed on the surface thereof. When solar light is incident on a solar cell, electrons at a Fermi level in the dye absorb solar energy and are thus excited to an upper level at which electrons are not occupied. As such, vacancies at a lower level from which the electrons escape are occupied again by supplying electrons from ions in the electrolyte. The ions which supply electrons to the dye are transferred to the counter electrode and thus receive electrons.
The counter electrode which is the cathode acts as a catalyst for a redox reaction of ions in the electrolyte so that electrons are supplied to the ions of the electrolyte via the redox reaction on the surface thereof.
In order to increase energy conversion efficiency of a dye-sensitized solar cell, a Pt thin-film having superior catalytic activity is mainly used, and a precious metal such as Pd, Ag, Au, etc., having characteristics similar to those of Pt, and a carbonaceous material such as carbon black or graphite may be utilized in the electrode.
The transparent glass substrate transports electrons to an external circuit while enabling absorption of solar energy and is typically formed of a transparent conductive oxide (TCO). Because an absorber layer on which solar light is incident to emit electrons and holes has to be covered with an electrode, its functions cannot exhibit or its efficiency may decrease when light is blocked by the electrode. For this reason, the TCO is used.
In particular, the TCO mainly includes FTO (Fluoride-doped Tin Oxide, Sn(F)O2).
However, such an FTO thin-film is deposited using an expensive device such as a large chemical vapor deposition device, undesirably resulting in complicated processes and increased manufacturing costs. Furthermore, the source materials therefor are patented in Japan's leading companies and universities, and all of them are currently imported.
The porous membrane formed on the FTO thin-film via screen printing using TiO2 nanoparticles has many defects at the inside and the surface of the particles because of characteristics of the nanoparticles, and thus scattering of electrons and recombination of electrons-holes may reduce the electron mobility and the electron lifetime, undesirably lowering electronic conductivity and resulting in low efficiency.
In the case of FTO, because surface characteristics between FTO and a Ti:Dye layer formed thereon become poor, solar cell efficiency may decrease, and upon bending a flexible dye-sensitized solar cell, the TCO and the absorber layer may be easily stripped off.
Hence, there is a need for a novel flexible transparent electrode for a dye-sensitized solar cell, which may exhibit high transmittance and low surface resistance to the extent that it may be used in lieu of FTO, may be formed via deposition at room temperature or low temperature on a plastic substrate, and may improve surface characteristics with a Ti:Dye layer.